Pigs have been an integral part of maintaining pipelines since the beginning of the 20th century.
The earliest devices were basic utility pigs, better known as scraper pigs. Updated versions are still in use today, scraping and scrubbing pipes to remove liquid and solid buildup.
Since 1965, oil pipeline operators have used technologically advanced versions that measure and record problems in the pipes. Known as “smart pigs,” these mechanical devices check for potential problems such as corrosion, dents, and cracks and provide information to a pipeline operator so that corrective measures can be taken.
Smart pigs are vital because of the thousands of miles of underground oil pipelines in the U.S. that are required to be inspected. Smart pigs are cylinder-shaped electronic devices inserted into the pipe and then propelled by the flowing oil. They detect loss of metal or deformations in the pipeline. Pipeline operators use this data to determine where potential problems are, which are then investigated further and repaired as needed.
New technologies have made smart pigs even more efficient and effective. Pigs that use magnetic flux leakage (MFL) technology, ultrasonic measurements and geometric tools are among the most common smart pigs used today.
There are two types of MFL technologies in use: standard and transverse flux inspection (TFI). TFI operates the same way as standard MFL, except that the magnetic field it generates is turned 90 degrees. Standard MFL pigs are best at detecting cracks and other defects while TFI pigs are better at detecting seam-related corrosion.
MFL can detect corrosion by sensing magnetic leakage. First, it initiates a magnetic field in the pipeline. If there are any flaws in the pipeline wall, some of the magnetic field will escape. Sensors onboard the pigs detect and measure that leakage. Smart pigs equipped with MFL technology can determine whether the corrosion is internal or external, and they can also measure for changes in the thickness of the walls.
Measurements are made when the pigs emit ultrasonic signals whose echoes are timed and compared with data to determine the wall’s thickness. The same ultrasonic technology can detect longitudinal cracks, crack-like defects, and longitudinal weld defects.
Smart pigs can also identify deformations, dents or obstructions by measuring the bore of the pipe for uniformity. These tools utilize mechanical arms or electro-mechanical instruments.
Smart pigs allow oil pipeline companies to comply more efficiently with the Pipeline Safety Improvement Act, strengthen reliability and safety, plus they increase the life of the pipeline.
